[type-annos-observers] ordering of annotated array brackets

[Timo Kinnunen]

Hi, 


I can’t help thinking that none of what’s being discussed would actually matter if there was a syntactically legal way to write something like this and doing anything else was deemed ambiguous:


@A (T[]) arr1; 


(@A T)[] arr2;
​

(more realistically perhaps @Length(10)<T[]> arr1 and <@NotNull T>[] arr2, in an alternate reality)





And then there’s the disquieting doubt about whether the syntax changes that would allow 


    @B ((@C ((@A T)[]))[]) arrList3;     (more realistically  @B <@C <@A T>[]>[] arrList3;  )


might in the end have turned out smaller than and obviating the need for the syntax changes needed to allow 

    T @A[] 

and 

    org.foo. @A T 

both.


I know, I know, “it’s too late for Java 8”, it was too late last year when I first started paying attention and probably has been too late since after 2009 when lambda syntax was decided. Hopefully it’s not yet too late for Java 10.




-- 
Have a nice day,
Timo.

Sent from Windows Mail





From: Markus Keller
Sent: ‎Wednesday‎, ‎March‎ ‎5‎, ‎2014 ‎12‎:‎26
To: type-annotations-spec-observers at openjdk.java.net
Cc: alex.buckley at oracle.com





Alex Buckley <alex.buckley at oracle.com> wrote on 2014-03-05 00:13:37:
> I disagree where post-identifier brackets are concerned, because I think 

> that adding them should not cause the reader to do gymnastics on the 
> annotated array type. It's simply astonishing that post-identifier [] 
> pairs are inserted _before_ the normal [] pairs. I keep recalling the 
> beauty of:
> 
> @A T   x;
> @A T[] y;
> 
> whereby adding [] doesn't affect anything to the left of []; in that 
> vein, adding @C [] should not affect anything to the left @B [].
> 
> @A T @B [] arr1;
> @A T @B [] arr2 @C [];

Note that this is not just about post-identifier [] pairs. It's a direct 
consequence of the notation for multi-dimensional array types.

If you have a declaration

  @A T @B [] @C [] arr3;

then arr3 is of type "@B-array of @C-array of @A T", and the component 
type of arr3 is

  @A T @C [] arr3component = arr3[7];

because "@B []" is the outermost dimension. This is a bit surprising, but 
as argued in [1], the surprise is that array brackets have to be written 
after the element type, and not before. Using a generic List "@B-List of 
@C-List of @A T", a similar type would look like this:

  @B List<@C List<@A T>> arrList3;

See how the order of annotations is @B, @C as well when @B is the 
outermost type annotation?

[1] 
http://types.cs.washington.edu/jsr308/specification/java-annotation-design.html#array-syntax

Markus